1. Technical Field of the Invention
The present invention relates to a liquid crystal display device comprising a patterned color filter layer and optically anisotropic layer on a surface such as a liquid crystal cell substrate, and a process for producing the same. The present invention also relates to a color filter plate comprising a patterned color filter layer and optically anisotropic layer, and a process for producing the same.
2. Related Art
A CRT (cathode ray tube) has been mainly employed in various display devices used for office automation (OA) equipment such as a word processor, a notebook-sized personal computer and a personal computer monitor, mobile phone terminal and television set. A liquid crystal display device (LCD) has been more and more widely used instead of a CRT, because it has a thin shape, lightweight and small electric power consumption. A liquid crystal display device comprises, at least, a liquid crystal cell and a polarizing plate. In general, a polarizing plate is produced by laminating the both surfaces of a polarizing film, which is prepared by soaking a polyvinyl alcohol film with iodine and then subjecting the same to stretching, with protective films, and, therefore, comprises a pair of protective films and a polarizing film.
For example, a transmissive LCD comprises two polarizing plates disposed on both sides of a liquid crystal cell, and may further comprise one or more optical compensatory sheets. On the other hand, a reflective LCD comprises a reflecting plate, a liquid crystal cell, one or more optical compensatory sheets, and a polarizing plate which are disposed in this order. A liquid crystal cell comprises a liquid crystal layer confined between two substrates, and electrode layers for applying a voltage to the liquid crystal layer. A liquid crystal cell has ON and OFF states on the basis of the difference in alignment state of the liquid crystal layer, and can be used in any of a transmissive type, reflective type and semi-transmissive type display devices employing any ever proposed modes such as TN (Twisted Nematic), IPS (In-Plane Switching), OCB (Optically Compensatory Bend), VA (Vertically Aligned), ECB (Electrically Controlled Birefringence) and STN (Super Twisted Nematic). Color and contrast displayed by the conventional liquid crystal display device, however, vary depending on the viewing angle. Therefore, it cannot be said that the viewing angle characteristics of the liquid crystal display device is superior to those of the CRT.
In order to improve the viewing angle properties, a retardation plate (optical compensatory sheet) has been employed for compensating birefringence generated depending on viewing angles. Till now, there has been proposed an LCD having an excellent viewing angle property of contrast by employing optical compensatory sheets having various optical properties for aforementioned wide-ranging display modes. In particular, three modes of OCB, VA and IPS have lead to have wide viewing angle properties in terms of contrast over the all directions as a wide viewing angle mode, and they have already been in widespread use as TV application for household use. Further, recently, large-sized displays of more than 30 inches have been provided.
Wide-screen LCDs suffer from light leakages from the corner portions, or, in other words, corner non-uniformities. It is considered that such phenomenon is caused by dimensional changes in the polarizer plates, which are employed in the LCDs, depending on environmental moisture. In particular for the case where a polarizer plate and an optical compensation sheet are bonded directly or bonded with an adhesive layer disposed between them, the optical compensation sheet may be changed in dimension with the polarizer plate, and, therefore, the optical characteristics of the optical compensation sheet may be varied with the dimensional change. And, in such a case, the corner non-uniformity may be worsened.
An optical compensation sheet can effectively contribute to reducing the viewing angle dependence of contrast, but cannot contribute to reducing the viewing angle dependence of color sufficiently, and reducing the viewing angle dependence of color is considered as an important problem to be solved for LCD. Viewing angle dependence of color of LCD is ascribable to difference in wavelength of three representative colors of R, G and B. Even R, G and B lights are given equal retardation, the changes in polarization states of R, G and B lights are different each other. For overcoming such problems, it is necessary to optimize wavelength dispersion of birefringence of an optically anisotropic material with respect to each of wavelengths of R, G and B. The LCD is, however, still on the way to thorough improvement in the viewing angle dependence of color, because it is still not easy to control the wavelength dispersion of birefringence of liquid crystal molecules used for ON/OFF display, or for optical compensation sheet.
There is proposed a retardation plate using a modified polycarbonate as an optical compensatory sheet in which the birefringence wavelength dispersion is controlled for the viewing angle property of color (Japanese Laid-Open Patent Publication (Tokkai), hereinafter referred to as “JPA”, No. 2004-37837). By using this for a λ/4 plate in a reflective liquid crystal display device or an optical compensatory sheet in the VA mode, the viewing angle property of color can be improved. However, modified polycarbonate film has not been used widely for LCDs yet due to such reasons that, not only the raw material itself is expensive, but also the unevenness in optical properties such as bowing occurs in stretching used in the manufacturing process thereof.
On the contrary, a system has been proposed, which has the same principle as that for the viewing angle compensation in terms of contrast by an optical compensatory sheet, but compensates it independently for three colors of R, G, B (e.g., GB 2394718, JPA Nos. 2004-240102, 2005-4124, 2005-24919, 2005-24920 and 2006-78647). This can be mainly realized by a method in which a retardation plate is patterned along with a color filter etc. in a liquid crystal cell. However, in order to pattern a retardation plate in a liquid crystal cell, for example, such troublesome operations are required, in the cell, as formation of an alignment film layer, rubbing treatment, coating, alignment and stabilization of a polymerizable liquid crystal composition, formation, etching treatment of a resist layer, and elimination by peeling of the resist layer. Consequently, it is difficult to form an optically anisotropic layer having an optically uniform retardation property. In addition, there is such problem that the retardation of a retardation plate changes before and after the etching due to heat and a solvent of the photo resist that are resulted upon forming the resist pattern.
On the other hand, as a method for producing a color filter, an ink jet system is known. In an ink jet system, an ink is ejected while moving an ink jet head lying above a transparent substrate to form patterns directly, therefore no exposure and development processes are required. Consequently, in an ink jet system, the reduction in a use amount of ink and the simplification of process allow the cost to be reduced. Therefore, the ink jet system attracts attention now as a method for producing a color filter. And the process for producing an optically anisotropic layer employing such ink jet system has been also provided (JPA No. 2006-64858).